The invention relates to a method for the automatic determination of the wheel base of steerable vehicles, particularly road vehicles, as well as to a device.
The handling of vehicles during braking operations could be improved considerably by the use of electronic automatic control systems. For achieving optimal braking decelerations, it is required, particularly in the case of trucks, to distribute a braking force, defined by the driver by the brake pedal, according to the momentary axle load to the individual wheels of the front and rear axle. This is achieved by the use of ALB devices (automatic load-dependent brake-force distribution devices) or, when EBS systems (electronic brake control systems) are used, by the use of load sensors. It is also endeavored in the case of tractor-trailer units to distribute the braking force defined by the driver optimally to the tractor vehicle and to the trailer vehicle in order to minimize the coupling forces, that is, the pulling and running-up forces acting between the two vehicles. A process for determining the running-up forces exerted by the trailer vehicle on the tractor vehicle is known from German Patent Document DE 43 13 198 C2. Corresponding to U.S. Pat. No. 5,477,739, in the case of this process, the distances of the two axles from the center of gravity of the tractor vehicle are calculated in the non-accelerated vehicle connection from the measured axle loads and a given wheel base of the tractor vehicle. The wheel base of the tractor vehicle is the distance between its front and rear axle. In order to further improve the handling of vehicles, the dynamic distribution of the axle loads--that is, the axle load distribution in the case of a braked or accelerated vehicle--can additionally be taken into account. If this is to take place in a computerized manner, for example, by using a microprocessor and calculating the dynamic axle load distribution from a measured static axle load distribution and a momentary vehicle deceleration, the knowledge of the wheel base is required also for this purpose.
A method and a device, for example, a computer system with integrated software, would therefore be desirable which automatically determines the wheel base of a vehicle. For economic reasons, it would also be desirable for the method and the device to be suitable for determining the wheel base of different vehicles or of different vehicle types.
It is therefore an object of the invention to provide a method and a device by which the wheel base of vehicles can be determined automatically.
The invention is based on the recognition that the wheel base of a steerable vehicle can be determined during stable cornering by means of the possibly different track widths of individual vehicle axles, the wheel circumference speeds and/or by means of steering angles of the steerable vehicle wheels. In this case, stable cornering is a cornering during which all wheels of the vehicle roll as precisely as possible on the road; that is, during which only low longitudinal and lateral slip values and low traction and braking values occur at the wheels.
The wheel base of a vehicle can therefore be determined exclusively from measured wheel circumference speeds and/or measured steering angles as well as defined track widths which may differ according to the vehicle. The track width is the mean distance between the "right" and the "left" wheel or twin wheel of a vehicle axle. For determining the wheel base according to the invention, the possibly different track widths of the individual vehicle axles are defined which, in the case of many trucks, have approximately the same value and can therefore be used as a constant for many cases.
The determination of the wheel circumference speeds can be carried out by rotational wheel speed sensors which exist already in vehicles equipped with an antilock system. Thus, the derermination of the base wheel base is possible merely using of sensors which exist already in modern vehicles. According to the vehicle type (tractor vehicle, trailer vehicle, semitrailer, etc.), a certain minimum number of wheel speed sensors is required for determining the wheel base.
If the vehicle is equipped with rotational wheel speed sensors on more wheels than required for determining the wheel base, a "redundant" wheel base computing is conceivable, using different "sensor groups", so that the obtained results can be compared.
If a vehicle is equipped with steering angle sensors on its steerable wheels, this may be used either exclusively or in combination with the rotational wheel speed sensors and the track width for determining the wheel base.
A wheel base determined by the method according to the invention and a signal representing the wheel base which is determined by the device according to the invention can be supplied to other control or automatic control devices, such as an automatic driving dynamics control, an antilock system, an electronic braking control system, etc., for further processing.